In some cases ArcGIS Server Post Installation does not run through successfully or does give a message that it has finished successfully but in reality has not set all needed access rights properly.
A quick check if presumably ArcGIS Server Post Installation has run through successfully is to have a look on the file access rights of local users ArcGIS Server Object Container Account (ArcGISSOC) and ArcGIS Server Object Manager Account (ArcGISSOM) on the ArcGIS Server location directory.
Both must have Full access rights on this directory and subdirectories.

File system access rights of local users ArcGISSOC and ArcGISSOM
In case these access rights are not set properly on your system then please check:
http://resources.arcgis.com/content/kbase?fa=articleShow&d=36535
If this knowledge base does not provide a solution for you then check your ArcGIS Server installation, refer to Online Knowledgebase (http://support.esri.com) or contact local Esri support for fixing this problem.